Burner assembly with dual register and throat construction

ABSTRACT

The formation of nitric oxide is reduced in the furnace section of a vapor generator by providing a throat construction coaxially mounted in the burner ports and utilizing two separate registers.

United States Patent Jaeger July 3, 1973 BURNER ASSEMBLY WITH DUAL2.217,518 10/1940 Merkt 431/115 X 2,271,587 2/1942 Haynes 431/184REGISTER AND THROAT CONSTRUCTION 3,335,782 8/1967 De Livois..... 431/115X n n r: Kurt Ja g Hurst, 3,146,821 9/1964 Wuetig 431/115 x [73]Assignee: Forney Engineering Company,

Dallas Primary Examiner-Edward G. Favors [22] Filed: June 15, 1971Attorney-John Maier, 111, Marvin A. Naigur et a1.

[2]] Appl. No; 153,306

52 US. Cl. 431/115, 431/188 ABSTRACT [51] Int. Cl. F231 7/00 [53] Fieldof Search 431/181, 182, 184, The formation of nitric oxide is reduced inthe furnace 3 /1 1 1 6 section of a vapor generator by providing athroat construction coaxially mounted in the burner ports and uti- [56]References Cited lizing two separate registers.

UNITED STATES PATENTS 1,754,433 4/1930 Peabody 431/188 6 Claims, 2Drawing Figures PATENIEBJIIL 3 I875 I INVENIOR.

. KURT S. JAEGER BY Z ATTORN Y BURNER ASSEMBLY WITH DUAL REGISTER ANDTHROAT CONSTRUCTION BACKGROUND OF THE INVENTION In the generation ofpower from fossil fuels, there has 5 been a great deal of interest inreducing pollutants in the form of oxides of nitrogen which are expelledinto the atmosphere. The problem can be better appreciated byconsidering the basic chemistry involved in the formation of nitrogenoxides in which the two critical l0 aspects for enhancing the reactionare increasing the temperature and adding excess amounts of oxygen.Accordingly, the formation of nitrogen oxides can be reduced in largevapor generators by recirculating flue gases or other inert gases intothe combustion zone,

such that the temperatures and combustion time are reduced, therebyreducing the content of nitrogen oxides in the resultant products ofcombustion. Also, by the mixing of inert gases with the combustion air,the

effective percentage of oxygen in the combustion air is substantiallyreduced, thereby further impeding the chemical reaction which results inthe formation of nitrogen oxides.

It has been found that by merely adding large amounts of inert gasesthrough the conventional burner locities which accompany theintroduction of inert gases into conventional burner constructions,results in a flame of marginal stability.

The instant dual throat and register design was developed to provide forbetter flame stability, lower wind box and furnace pressuredifierentials, better flame detection conditions, and maximum burneradjustability, while reducing the temperature and amount of oxygenpresent in the combustion area in order to reduce the formation ofnitrogen oxides. Thus, in accordance with the present invention it ispossible to obtain acceptable burner operation from fuel systems usinggas and/or oil when the vapor generator is operated in such a manner asto minimize the nitrogen oxides formed in flue gases. Accordingly,through the present invention it is possible to recirculate the fluegases and combine them with the combustion air or to separately feed theflue gases into the combustion zone. Furthermore, the dual throat andregister design of the present invention can accommodate theconventional burner structure presently in operation, and still achievedesirable high throat velocities, while handling the relatively largequantities of combustion air required for nitrogen oxide reductionwithout producing excessively high wind box to furnace differentialpressures. 60

SUMMARY OF THE INVENTION In accordance with an illustrative embodimentdemonstrating features and advantages of the present invention, there isprovided an apparatus for reducing the 65 ings for introducing a streamof products of combustion into the furnace and an enclosure surroundsthe burners for conveying substantially inert gases to the portopenings. The instant apparatus comprises throat means surrounding eachof the burners coaxially mounted in each of the port openings to form anannular passageway, with primary register means movably mounted in theenclosure between each of the burners and associated throat means. Asecondary register means is movably mounted in the enclosure betweeneach of the throat means and associated port opening. Accordingly, thestream of gases is divided into a primary stream which is directly mixedwith the stream of products of combustion and a secondary annular gassheath which is passed through the annular passageway and exhaustedbeyond the throat means to surround the stream of products of combustionsuch that the temperature and oxygen content of the stream of prodactsof combustion is reduced and the formation of nitrogen oxides isretarded.

BRIEF DESCRIPTION OF THE DRAWINGS The above brief description, as wellas further objects, features, and advantages of the present inventionwill be more fully appreciated by reference to the following detaileddescription of presently preferred embodiments, when taken in connectionwith the accompanying drawings wherein:

FIG. 1 is a sectional view showing the overall furnace 0 and wind boxsetting of the vapor generator with the dual throat and register andupper rows of burners being shown schematically, and with the embodimentutilizing a single source of primary and second air being illustrated;

FIG. 2 is a sectional view taken through wind box an port opening in thevicinity of the lower left burner of the vapor generator shown in FIG.1, with a further embodiment also being shown in which a separate sourceof secondary air is illustrated.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now specifically tothe drawings, there is shown schematically in FIG. 1 a vapor generatorfurnace section 10 which is provided with a dual throatdual registersystem embodying features of the present invention and generallydesignated by the reference numeral 12. The furnace section 10 is formedfrom heat absorption tubular walls 14 having port openings 16 forintroducing a stream of products of combustion into the furnace section10. The combined dual throat and register system 12 is designed toaccommodate a conventional burner 18. The tubular walls 14 arecoextensively covered with an outer wall 22, and for the sake ofconvenience the header system and other portions of the vapor generatorhave not been shown in the drawings. Mounted exteriorly with respect tothe furnace section 10 is a wind box enclosure 24 which surrounds thedual throat-register system l2and burners 18. A duct system 26 isconnected in flow communication with the wind box enclosure 24 and asource of substantially inert gases which have not been shown in thedrawings. The stream of inert gases has been designated by thedirectional arrows 28, and it has been generally contemplated that thiswould comprise flue gas from the burner stack, and also possibly airfrom the preheater which could also be mixed with the flue gas dependingon the operating conditions of the vapor generator.

Turning to FIG. 2, the burner 18 is shown in greater detail andcomprises a cylindrical housing 30 in which there is mounted a pair ofgas guns 32, an oil gun 34, and an ignitor 36. The wind box enclosure 24is formed by a casing wall 40 which defines an interior housing 42, suchthat the burner 18 extends through casing wall 40 into interior housing42. A duct collar 44 and associated damper 46 are mounted on the burnerhousing 30 for introducing a portion of the inert gas stream 28 directlyinto the burner 30.

It should be understood that the embodiment of the dual register andthroat construction 12 shown in'"FIG. 1, contemplates a single source,whereas the embodiment shown in FIG. 2 contemplates a wind box enclosure24 with two separate sources for gas stream 28. The differences betweenthe modification to the wind box enclosure of FIG. 2 will be more fullyoutlined, but it should be understood that the schematic showing of thedual register and throat construction 12 in FIG. 1 is consistent withthe detailed showing in FIG. 2, and that the same numbers will be usedto designate like parts in FIG. 1 and FIG. 2.

By referring to FIG. 1, it can be appreciated that dual register andthroat construction 12 comprises a throat means 50 surrounding each ofthe burners 18 and coaxially mounted in each of the port openings 16 toform an annular passageway 52. A primary register 54 is movably mountedin the wind box enclosure 24 between the burner 18 and throatconstruction 50, while a secondary register 56 is movably mounted inwind box enclosure 24 between the throat construction 50 and portopenings 16. Accordingly, the stream of gases 28 is divided into aprimary stream, denoted by the arrows 57, which is directly mixed withthe products of combustion and a secondary annular gas sheath denoted bythe arrows 58 which is passed through the annular passageway 52 andexhausted beyond the throat construction 50 to surround the products ofcombustion 20. In this manner, the temperature and oxygen content of theproducts of combustion 20 are reduced and the formation of nitrogenoxides is retarded.

Turning back to FIG. 2 the heat absorption walls 14 are formed from aconventional fin-tube wall construction 60, and the port openings 16 areformed by transversely bending the fin tube wall 60. An annularinsulation collar 62 is mounted in the port openings 16, and theinterior wall of the insulation collar 62 defines a throat area whichhas been generally designated 64. The outer wall 22 includes insulationmaterial 66 and an outer metallic skin casing 68 which are coextensivewith respect to the fin tube wall 60.

The throat construction 50 includes a throat ring 70 integrally formedwith a frustoconical collar 72 and an annular shoulder 74, which iscoaxially positioned in the throat area 64 by means of a mounting plate76. Accordingly, the annular shoulder 74 is welded to the mounting plate76 which is in turn mounted to the outer casing 68 by means of thesecondary register 56. This is achieved by securing an annular mountingplate 80, having an L shaped cross-section to the outer casing 68 andmounting annular plate 76 in a position which is spaced apart from theplate 80. The secondary register 56 which includes a series of vanesjournaled between the plates 76 and 80, can serve as the actual means ofmounting the plate 76, but it is possible to utilize separate supportswhich are horizontally disposed with respect to plate 76 and have notbeen shown in the drawings. The vanes 82 are of a conventionalconstruction and are journaled by means of shafts 84 which in turn areusually operatively connected to a conventional linkage arrangement formoving the vanes 82 from various settings from an open to a closedposition such that the gas flow through the annular space 52 can beadjusted.

A mounting ring 86 is welded to plate 76 for supporting an annularbracket 88 which is provided for mounting the secondary register 54.This is achieved by securing an outer plate 90 to the burner housing 30in a position spaced apart from the bracket 88. Accordingly, the primaryregister 54 which is provided with a series of main vanes 92 isjournaled between the bracket 88 and the outer plate 90. As in the caseof the secondary register 56, the main vanes 92 are journaled around theperiphery of the primary register 54 by means of a series of shafts 94,which are likewise provided with a conventional linkage system which hasnot been shown in the drawings, for operating the main vanes 92 betweenan open and closed position. A heat shield 96 is mounted to the outerplate 90 by brackets 98.

It can be appreciated that the embodiment shown in FIG. 2 differs fromthat of FIG. 1, in that the casing wall 40 of FIG. 2 is mounted on anauxiliary wind box 100 instead of the outer wall 22 as in FIG. 1. Thus,as schematically shown in FIG. 2, the auxiliary wind box 100 includes anenclosure wall 102 which is mounted to the skin casing 68 for housingthe secondary register 56. In this manner, the duct system 26 conveysthe inert gas stream 28 to interior housing 42 of the wind box 40 and asecondary inert gas stream designated by the directional arrows 104 isconveyed into auxiliary wind box 100. Accordingly, in the FIG. 1embodiment of the instant invention, the inert gas stream 28 serves boththe primary register 54 and secondary register 56, while in the FIG. 2embodiment the inert gas stream 28 flows through primary register 54 andsecondary inert gas stream 104 flows through secondary register 56.Thus, in the FIG. 2 embodiment the annular gas sheath 58 is formed fromthe secondary inert gas stream 104, and the primary stream 57 is formedby the inert gas stream A latitude of modification, change andsubstitution is intended in the foregoing disclosure and in someinstances some features of the invention will be employed without acorresponding use of other features. Accordingly, it is appropriate thatthe appended claims be construed broadly and in a manner consistent withthe spirit and scope of the invention herein.

What is claimed is:

1. Apparatus for reducing the temperature in the furnace section of avapor generator formed with heat absorption tubular walls having portopenings, comprising a plurality of burners mounted adjacent said portopenings, each of said burners formed with a cylindrical wall having anexhaust aperture for introducing a stream of products of combustion intosaid furnace, an enclosure surrounding said burners for conveyingsubstantially inert gases to said port openings, said cylindrical wallhaving an orifice for introducing a portion of said inert gases to saidburners, throat means surrounding each of said burners coaxially mountedin each of said port openings to form an annular passageway, primaryregister means movably mounted in said enclosure between each of saidburners and associated throat means and secondary register means movablymounted in said enclosure between each of said throat means andassociated port opening, whereby said inert gases are divided into aprimary stream which is directly mixed with said stream of products ofcombustion and a secondary annular gas sheath which is passed throughsaid annular passageway and exhausted beyond said throat means tosurround said stream of products of combustion such that the temperatureand oxygen content of said stream of products of combustion is reducedand the formation of nitrogen oxides is retarded.

2. Apparatus according to claim 1 in which said enclosure conveys saidstream of gases to said primary register means and said secondaryregister means.

3. Apparatus according to claim 1, in which said enclosure includes asecondary wind box mounted on said furnace and in flow communicationwith said secondary register means, and a main wind box mounted on saidsecondary wind box in flow communication with said primary registermeans.

4. Apparatus according to claim 1 in which said throat means includes athroat ring integrally formed with a frustoconical collar, said primaryregister means includes a series of vanes movably mounted between eachof said burners and associated collar, and said secondary register meansincludes a series of vanes movably mounted between the exterior of saidwalls and said collar.

5. Apparatus for reducing the temperature in the furnace section of avapor generator formed with heat absorption tubular walls having portopenings, comprising a plurality of burners mounted adjacent said portopenings, each of said burners formed with a cylindrical wall having anexhaust aperture for introducing a stream of products of combustion intosaid furnace, an enclosure surrounding said burners" for conveyingsubstantially inert gases to said port openings, throat meanssurrounding each of said burners coaxially mounted in each of said portopenings to form an annular passageway, primary register means movablymounted in said enclosure between each of said burners and associatedthroat means and secondary register means movably mounted in saidenclosure between each of said throat means and associated port opening,said enclosure including a secondary wind box mounted on said furnaceand in flow communication with said secondary register means, and a mainwind box mounted on said secondary wind box in flow communication withsaid primary register means, whereby said inert gases are divided into aprimary stream which is passed through said main wind box and directlymixed with said stream of products of combustion and a secondary annulargas sheath from said secondary wind box which is passed through saidannular passageway and exhausted beyond said throat means to surroundsaid stream of products of combustion such that the temperature andoxygen content of said stream of products of combustion is reduced andthe formation of nitrogen oxides is retarded.

6. Apparatus according to claim 5 in which said throat means includes athroat ring integrally formed with a frustoconical collar, said primaryregister means includes a series of vanes movably mounted between eachof said burners and associated collar, and said secondary register meansincludes a series of vanes movably mounted between the exterior of saidwalls and said collar.

1. Apparatus for reducing the temperature in the furnace section of avapor generator formed with heat absorption tubular walls having portopenings, comprising a plurality of burners mounted adjacent said portopenings, each of said burners formed with a cylindrical wall having anexhaust aperture for introducing a stream of products of combustion intosaid furnace, an enclosure surrounding said burners for conveyingsubstantially inert gases to said port openings, said cylindrical wallhaving an orifice for introducing a portion of said inert gases to saidburners, throat means surrounding each of said burners coaxially mountedin each of said port openings to form an annular passageway, primaryregister means movably mounted in said enclosure between each of saidburners and associated throat means and secondary register means movablymounted in said enclosure between each of said throat means andassociated port opening, whereby said inert gases are divided into aprimary stream which is directly mixed with said stream of products ofcombustion and a secondary annular gas sheath which is passed throughsaid annular passageway and exhausted beyond said throat means tosurround said stream of products of combustion such that the temperatureand oxygen content of said stream of products of combustion is reducedand the formation of nitrogen oxides is retarded.
 2. Apparatus accordingto claim 1 in which said enclosure conveys said stream of gases to saidprimary register means and said secondary register means.
 3. Apparatusaccording to claim 1, in which said enclosure includes a secondary windbox mounted on said furnace and in flow communication with saidsecondary register means, and a main wind box mounted on said secondarywind box in flow communication with said primary register means. 4.Apparatus according to claim 1 in which said throat means includes athroat ring integrally formed with a frustoconical collar, said primaryregister means includes a series of vanes movably mounted between eachof said burners and associated collar, and said secondary register meansincludes a series of vanes movably mounted between the exterior of saidwalls and said collar.
 5. Apparatus for reducing the temperature in thefurnace section of a vapor generator formed with heat absorption tubularwalls having port openings, comprising a plurality of burners mountedadjacent said port openings, each of said burners formed with acylindrical wall havIng an exhaust aperture for introducing a stream ofproducts of combustion into said furnace, an enclosure surrounding saidburners for conveying substantially inert gases to said port openings,throat means surrounding each of said burners coaxially mounted in eachof said port openings to form an annular passageway, primary registermeans movably mounted in said enclosure between each of said burners andassociated throat means and secondary register means movably mounted insaid enclosure between each of said throat means and associated portopening, said enclosure including a secondary wind box mounted on saidfurnace and in flow communication with said secondary register means,and a main wind box mounted on said secondary wind box in flowcommunication with said primary register means, whereby said inert gasesare divided into a primary stream which is passed through said main windbox and directly mixed with said stream of products of combustion and asecondary annular gas sheath from said secondary wind box which ispassed through said annular passageway and exhausted beyond said throatmeans to surround said stream of products of combustion such that thetemperature and oxygen content of said stream of products of combustionis reduced and the formation of nitrogen oxides is retarded. 6.Apparatus according to claim 5 in which said throat means includes athroat ring integrally formed with a frustoconical collar, said primaryregister means includes a series of vanes movably mounted between eachof said burners and associated collar, and said secondary register meansincludes a series of vanes movably mounted between the exterior of saidwalls and said collar.